This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Epidemiological studies demonstrate an inverse correlation with prostate cancer incidence and increased consumption of soy products (16) as well as increased exposure to vitamin D (either from fish oils or UV irradiation) (17,18). Soy is rich in isoflavones such as genistein and daidzein, which are known to have antiproliferative effects on prostatic cells (see (19) for a review). Schwartz et. al., hypothesized that vitamin D deficiency increases the risk of prostate cancer (17). This hypothesis is supported by the demonstration that vitamin D exhibits an antiproliferative as well as a pro-differentiating influence on prostatic cells in vitro (20-24). Taken together, epidemiological and dietary data suggest that both soy and vitamin D play an important role in protecting against prostate cancer (25). Our published and preliminary data demonstrate strong synergistic growth inhibition of cultured human prostatic epithelial cells by the combination of the soy isoflavone genistein with various vitamin D compounds.(26) We hypothesize, therefore that a combination of vitamin D plus soy will be efficacious in treating biochemically recurrent prostate cancer.